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Dolcera Corporation Horizontal Axis Wind Turbines (HAWT)

Introduction:

Introduction Harnessing renewable alternative energy is the ideal way to tackle the energy crisis, with due consideration given to environmental pollution, that looms large over the world. Renewable energy is also called "clean energy" or "green power" because it doesn’t pollute the air or the water. Wind energy is one such renewable energy source that harnesses natural wind power. The development of wind energy systems and advances in power electronics, electric drives, control systems, have enabled eﬃcient future for wind energy. Wind generation through doubly fed induction generators connected to wind turbine is a very eﬀective way of generation. 5

HAWT Taxonomy:

HAWT Taxonomy 6 A detailed taxonomy is presented covering parts of the turbine, control systems, applications among others See the detailed HWAT taxonomy here

Taxonomy:

Taxonomy 13 Field is broken into subcategories on the basis of various parameters The resulting taxonomy is used to analyze existing literature as well as products in the field . Taxonomy

Patent Analysis:

Patent Analysis 14 Problem solution approach enables to map different problems and the available solutions Sample Patent Analysis S. No Patent/Publication No. Publication Date (mm/dd/yyyy) Assignee / Applicant Title Doclera Analysis Problem Solution 1 US20100117605 05/13/10 Woodward Method of and apparatus for operating a double-fed asynchronous machine in the event of transient mains voltage changes The short-circuit-like currents in the case of transient mains voltage changes lead to a corresponding air gap torque which loads the drive train and transmission lines can damages or reduces the drive train and power system equipments. The method presents that the stator connecting with the network and the rotor with a converter. The converter is formed to set a reference value of an electrical amplitude in the rotor, by which a reference value of the electrical amplitude is setted in the rotor after attaining a transient mains voltage change, such that the rotor flux approaches the stator flux. 2 US20100045040 02/25/10 Vestas Wind Systems Variable speed wind turbine with doubly-fed induction generator compensated for varying rotor speed The DFIG system has poor damping of oscillations within the flux dynamics due to cross coupling between active and reactive currents, which makes the system potentially unstable under certain circumstances and complicates the work of the rotor current controller. These oscillations ca damage the drive train mechanisms. A comprensation block is arranged, which feeds a compensation control output to the rotor of the generator. The computation unit computes the control output during operation of the turbine to compensate partly for dependencies on a rotor angular speed of locations of poles of a generator transfer function, so that the transfer function is made independent of variations in the speed during operation of the turbine which eliminates the osicllations and increases the efficinecy of the wind turbine. 3 US20090267572 10/29/09 Woodward Current limitation for a double-fed asynchronous machine Abnormal currents can damage the widings in the doubly- fed induction gnerator . Cntrolling these currents with the subordinate current controllers cannot be an efficient way to extract the maximum amount of active power. The method involves delivering or receiving of a maximum permissible reference value of an active power during an operation of a double-fed asynchronous machine, where predetermined active power and reactive power reference values are limited to a calculated maximum permissible active and reactive power reference values, and hence ensures reliable regulated effect and reactive power without affecting the power adjustment, the rotor is electrically connected to a pulse-controlled inverter by slip rings with a static frequency changer, and thus a tension with variable amplitude and frequency is imposed in the rotor. 4 US20090008944 01/08/09 Universidad Publica De Navarra Method and system of control of the converter of an electricity generation facility connected to an electricity network in the presence of voltage sags in said network Double-fed asynchronous generators are very sensitive to the faults that may arise in the electricity network, such as voltage sags. During the sag conditions the current which appears in said converter may reach very high values, and may even destroy it. During the event of a voltage sag occurring, the converter imposes a new setpoint current which is the result of adding to the previous setpoint current a new term, called demagnetizing current, It is is proportional to a value of free flow of a generator stator. A difference between a value of a magnetic flow in the stator of the generator and a value of a stator flow associated to a direct component of a stator voltage is estimated. A value of a preset calculated difference is multiplied by a factor for producing the demagnetizing current. 5 US7355295 04/08/08 Ingeteam Energy Variable speed wind turbine having an exciter machine and a power converter not connected to the grid a) The active switching of the semiconductors of the grid side converter injects undesirable high frequency harmonics to the grid. b) The use of power electronic converters (4) connected to the grid (9) causes harmonic distortion of the network voltage. Providing the way that power is only delivered to the grid through the stator of the doubly fed induction generator, avoiding undesired harmonic distortion. Grid Flux Orientation (GFO) is used to accurately control the power injected to the grid. An advantage of this control system is that it does not depend on machine parameters, which may vary significantly, and theoretical machine models, avoiding the use of additional adjusting loops and achieving a better power quality fed into the utility grid. 6 US20080203978 08/28/08 Semikron Frequency converter for a double-fed asynchronous generator with variable power output and method for its operation Optislip circuit with a resistor is used when speed is above synchronous speed, results in heating the resistor and thus the generator leads to limitation of operation in supersynchronous range which results tower fluctions. Providing a back-to-back converter whic contains the inverter circuit has direct current (DC) inputs , DC outputs, and a rotor-rectifier connected to a rotor of a dual feed asynchronous generator. A mains inverter is connected to a power grid, and an intermediate circuit connects one of the DC inputs with the DC outputs. The intermediate circuit has a semiconductor switch between the DC outputs, an intermediate circuit condenser between the DC inputs, and a diode provided between the semiconductor switch and the condenser. Thus the sysem is allowed for any speed of wind and reduces the tower fluctuations. 7 US20070210651 09/13/07 Hitachi Power converter for doubly-fed power generator system During the ground faults, excess currents is induced in the secondary windings and flows into power converter connected o secondar side and may danage the power converter. Conventional methos of incresing the capacity of the power cnverter increases system cost , degrade the system and takes time to activate the system to supply power again. The generator provided with a excitation power converter connected to secondary windings of a doubly-fed generator via impedance e.g. reactor, and a diode rectifier connected in parallel to the second windings of the doubly-fed generator via another impedance. A direct current link of the rectifier is connected in parallel to a DC link of the converter. A controller outputs an on-command to a power semiconductor switching element of the converter if a value of current flowing in the power semiconductor switching element is a predetermined value or larger. 8 US20070132248 06/14/07 General Electric System and method of operating double fed induction generators Wind turbines with double fed induction generators are sensitive to grid faults.Conventional methods are not effective to reduce the shaft stress during grid faults and slow response and using dynamic vltage restoreer (DVR) is cost expensive. The protection system has controlled impedance devices.Impedance device has bidirectional semiconductors such triac, assembly of thyristors or anti-parallel thyristors. Each of the controlled impedance devices is coupled between a respective phase of a stator winding of a double fed induction generator and a respective phase of a grid side converter. The protection system also includes a controller configured for coupling and decoupling impedance in one or more of the controlled impedance devices in response to changes in utility grid voltage and a utility grid current. High impedance is offered to the grid during network faults to isolate the dual fed wind turbine generator. 9 US20060192390 08/31/06 Gamesa Innovation Control and protection of a doubly-fed induction generator system A short-circuit in the grid causes the generator to feed high stator-currents into the short-circuit and the rotor-currents increase very rapidly which cause damage to the power-electronic components of the converter connecting the rotor windings with the rotor-inverter. The converter is provided with a clamping unit which is triggered from a non-operation state to an operation state, during detection of over-current in the rotor windings. The clamping unit comprises passive voltage-dependent resistor element for providing a clamping voltage over the rotor windings when the clamping unit is triggered. 10 US20050189896 09/01/05 ABB Research Method for controlling doubly-fed machine Controlling the double fed machines on the basis of inveter control to implement the targets set for the machine, this model is extremely complicated and includes numerous parameters that are often to be determined. A method is provided to use a standard scalar-controlled frequency converter for machine control. A frequency reference for the inverter with a control circuit, and reactive power reference are set for the machine. An rotor current compensation reference is set based on reactive power reference and reactive power. A scalar-controlled inverter is controlled for producing voltage for the rotor of the machine, based on the set frequency reference and rotor current compensation reference.

Article Analysis:

Article Analysis 15 Novelty of the invention is captured in Dolcera summary Sample Article Analysis S No. Title Publication Date (mm/dd/yyyy) Journal/Conference Dolcera Summary 1 Study on the Control of DFIG and it's Responses to Grid Disturbances 01/01/06 Power Engineering Society General Meeting, 2006. IEEE Presented dynamic model of the DFIG, including mechanical model, generator model, and PWM voltage source converters. Vector control strategies adapted for both the RSC and GSC to control speed and reactive power independently. controlling designing methods, such as pole-placement method and the internal model control are used. Matlab/Simulink is used for simulation. 2 Application of Matrix Converter for Variable Speed Wind Turbine Driving an Doubly Fed Induction Generator 05/23/06 Power Electronics, Electrical Drives, Automation and Motion, 2006. SPEEDAM 2006. A matrix converter is replaced with back to back converter in a variable speed wind turbine using doubly fed induction generator. Stable operation is achieved by stator flux oriented control technique and the system operated in both sub and super synchronous modes, achieved good results. 3 Optimal Power Control Strategy of Maximizing Wind Energy Tracking and Conversion for VSCF Doubly Fed Induction Generator System 08/14/06 Power Electronics and Motion Control Conference, 2006. IPEMC 2006. CES/IEEE 5th International Proposed a new optimal control strategy of maximum wind power extraction strategies and testified by simulation. The control algorithm also used to minimize the losses in the generator. The dual passage excitation control strategy is applied to decouple the active and reactive powers. With this control system, the simulation results shows the good robustness and high generator efficiency is achieved. 4 A Torque Tracking Control algorithm for Doubly–fed Induction Generator 01/01/08 Journal of Electrical Engineering Proposed a torque tracking control algorithm for Doubly fed induction generator using PI controllers. It is achieved by controlling the rotor currents and using a stator voltage vector reference frame. 5 Fault Ride Through Capability Improvement Of Wind Farms Using Doubly Fed Induction Generator 09/04/08 Universities Power Engineering Conference, 2008. UPEC 2008. 43rd International An active diode bridge crowbar switch presented to improve fault ride through capability of DIFG . Showed different parameters related to crowbar such a crowbar resistance, power loss, temperature and time delay for deactivation during fault.

Dolcera Dashboard:

Market Overview:

Market Overview The total global wind power generation in the year 2009 shown below 18 Top 10 Cumulative Installed Capacity 2009

Market Forecast:

Market Forecast Global wind power capacity could reach 2,300 GW by 2030, providing up to 22% of the world's electricity needs, from the existing 2.2% in 2010. 19 Annual market forecast by region 2009-2013

Insights: Major Players:

Insights: Major Players Vestas Wind Energy Systems and General Electric are the major players in wind energy generation through doubly-fed induction generator technology . 20

Insights: Key Patents :

Insights: Key Patents Key patents in the field are held by US Windpower , Oregon State and Vestas Wind Energy Systems 21

Insights: Year wise IP activity:

Insights: Year wise IP activity Year wise IP activity based on publication years 22

Insights: Geographical Distribution:

Insights: Others:

Insights: Others Around 86% patents are on controlling the doubly-fed induction generation(DFIG) which indicates high research activity going on in rating and controlling of the DFIG systems. 86% of the patent on DFIG operation are focusing on grid connected mode of operation, suggesting continuous operation of the DFIG system during weak and storm winds, grid voltage sags, and grid faults are major issues in the current scenario. Woodward is a new and fast developing player in the field of DFIG technology. The company filed 10 patent applications in the field in year 2010, while it has no prior IP activity. 24